N-hexyl-3-methylimidazolium hexafluoro phosphate/multiwall carbon nanotubes paste electrode as a biosensor for voltammetric detection of morphine

A carbon paste electrode modified with multiwall carbon nanotubes (MWNTs) and room-temperature ionic liquid, n-hexyl-3-methylimidazolium hexafluoro phosphate was prepared. The electrochemistry of morphine at the surface of the modified electrode was studied using cyclic voltammetry, chronoamperometry, and electrochemical impedance spectroscopy (EIS). The cyclic voltammogram showed an irreversible oxidation peak at 0.48 V (vs. Ag/AgClsat), which corresponded to the oxidation of morphine. Compared to common carbon paste electrode, the electrochemical response was greatly improved. Under the optimized conditions, the oxidation peak current of morphine showed two linear dynamic ranges (in 0.6-600 mu mol L-1) with a detection limit of 0.02 mu mol L-1, using differential pulse voltammetry. The proposed sensor was successfully applied for the determination of morphine in biological and pharmaceutical samples such as human urine and injection solution. (C) 2012 Elsevier B.V. All rights reserved.